Fuel pump

ABSTRACT

A fuel pump  10  may be with a substantially disk-shaped impeller  20  and a casing  14  for housing the impeller  20  such that the impeller  20  can rotate. Permanent magnets  26  may be disposed in the impeller  20.  A driving coil  40  may be disposed in the casing  14  at a location opposite the permanent magnets  26.  The impeller  20  rotates when power is supplied to the driving coil  40.  The fuel pump  10  may include a supporting device  42  for supporting the impeller. The supporting device  42  may be located in at least one location in an inner face of the casing  14,  this inner face of the casing being located opposite an upper face, a lower face, and an outer peripheral face of the impeller  20.  It is preferred that the supporting device  42  has a rolling element that makes rolling contact with the impeller  20.

CROSS REFERENCE

This application claims priority to Japanese Patent application number 2004-142067, filed on May 12, 2004, the contents of which are hereby incorporated by reference as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fuel pump for drawing in a fuel such as gasoline etc., increasing the pressure thereof, and discharging this pressurized fuel.

2. Description of the Related Art

This type of fuel pump is used while disposed within a fuel tank. When the fuel pump will be disposed within a shallow and flat fuel tank, the fuel pump must be short in an axial direction (i.e., in a vertical direction). For this purpose, axial type fuel pumps have been developed (e.g., Japanese Un-Examined Utility Model Publication No. 6-70476).

This fuel pump is provided with a substantially disk-shaped impeller and a casing that houses the impeller. Permanent magnets are embedded in the impeller, and a driving coil is embedded in the casing. The driving coil is located opposite the permanent magnets of the impeller, and the impeller is rotated by passing current through the driving coil. In this fuel pump, the driving coil disposed in the casing directly rotates the impeller that has the permanent magnets embedded therein, and consequently the fuel pump can be made smaller in the axial direction.

SUMMARY OF THE INVENTION

However, in the fuel pump that utilizes an axial type motor structure, the diameter of the impeller is increased by the size of the permanent magnets. When the diameter of the impeller is greater, the impeller and the casing make contact if the impeller has even a small inclination. There is the problem that sliding resistance causes a fall in pump efficiency if the impeller and the casing make contact.

It is, accordingly, one object of the present teachings to provide an axial type fuel pump in which sliding resistance between an impeller and a casing is reduced, thereby increasing pump efficiency.

In one aspect of the present teachings, a fuel pump may comprise a substantially disk-shaped impeller, and a casing for housing the impeller such that the impeller can rotate within the casing. Permanent magnets may be disposed in the impeller. A driving coil may be disposed in the casing at a location opposite the permanent magnets. The impeller rotates when power is supplied to the driving coil. The fuel pump may have a driving circuit for supplying power to the driving coil. The driving circuit may convert direct power supplied from an exterior power supply into polyphase power, and supplies this to the driving coil. The driving coil generates magnetic force when power is supplied thereto, and this magnetic force rotates the impeller.

It is preferred that the fuel pump has a supporting device (e.g., a roller bearing or a ball bearing) for supporting the impeller. The supporting device may be located in at least one location in an inner face of the casing, this inner face of the casing being opposite an upper face, a lower face, and an outer peripheral face of the impeller. It is preferred that the supporting device has a rolling element that makes rolling contact with the impeller. When the supporting device is provided at the inner face of the casing, the impeller is supported by the supporting device even when the impeller would otherwise become inclined, and the inclination of the impeller is thus suppressed. Further, the impeller is supported by the rolling contact with the rolling element, and consequently there is low sliding resistance between the impeller and the supporting device. As a result, the impeller can rotate smoothly even though the impeller and the supporting device are making contact. Since the impeller can rotate smoothly in this fuel pump (since the sliding resistance between the impeller and the supporting device is low), pump efficiency can be increased.

Furthermore, a variety of elements can be used as the rolling element of the supporting device. For example, the following may be used a cylindrical roller, a long cylindrical roller, a tapered roller, a spherical roller, a barrel shaped roller, etc.

In another aspect of the present teachings, fuel may be sucked in at both an upper and a lower face of the impeller, and that fuel may be discharged from both the upper and the lower face of the impeller. For example, groups of concavities may be formed both the upper and the lower face of the impeller, and the group of concavities may be formed along the circumference direction of the impeller in an area in the vicinity of its outer circumference of the impeller. The permanent magnets may be disposed inwards with respect to the group of concavities. A first groove may be formed in the inner face of the casing opposite the upper face of the impeller, the first groove being formed in an area facing the group of concavities in the impeller and extending continuously in a circumference direction from an upstream end to a downstream end. A second groove may be formed in the inner face of the casing opposite the lower face of the impeller, the second groove being formed in an area facing the group of concavities in the impeller and extending continuously in a circumference direction from an upstream end to a downstream end. A fuel intake passage and a fuel discharge passage may be formed in the casing. The fuel intake passage communicates between the vicinity of the upstream end of the first groove and the exterior of the casing, and between the vicinity of the upstream end of the second groove and the exterior of the casing. The fuel discharge passage communicates between the vicinity of the downstream end of the first groove and the exterior of the casing, and between the vicinity of the downstream end of the second groove and the exterior of the casing. This type of configuration can reduce differences in fuel pressure exerted upon the upper and lower faces of the impeller, and consequently suppress inclination of the impeller.

Further, there may be communication between bottom portions of the pair of the upper concavities formed in the upper face of the impeller and the lower concavities formed in the lower face of the impeller. Moreover, it is preferred that the groups of concavities are formed in the upper and lower faces of the impeller in the areas located inwardly from the outer circumference of the impeller by a predetermined distance. In this configuration, a radial seal is not required, and consequently a space can be formed between the casing and the outer peripheral face of the impeller. Contact between the outer peripheral face of the impeller and the inner face of the casing is thus prevented.

In another aspect of the present teachings, the supporting device (e.g., a ball bearing) may be disposed in the fuel pump in both the inner face of the casing opposite the upper face of the impeller, and the inner face of the casing opposite the lower face of the impeller. It is preferred that the supporting device supports the impeller at an area outwards with respect to the region having the permanent magnets, and inwards with respect to the region having the recesses formed therein. Further, it is preferred that the supporting devices are disposed at a plurality of locations along the circumference direction of the impeller.

With this type of configuration, the upper and lower faces of the impeller are supported by the supporting device even when the impeller would otherwise become inclined. As a result, the inclination of the impeller can effectively be suppressed. Further, the supporting device supports the impeller at a region between the location where the magnetic force of the driving coil operates (i.e., the region where the permanent magnets are located), and the location where fuel pressure operates (i.e., the region where the concavities are formed). Consequently, thrust being operated on the impeller by the fuel pressure and the magnetic force of the driving coil can be received in a balanced manner by the supporting device.

In another aspect of the present teachings, the supporting device may be disposed in at least three locations in the inner face of the casing opposite the outer peripheral face of the impeller. With this type of configuration, at least three locations of the outer peripheral face of the impeller are supported by the supporting device, and consequently inclination of the impeller can effectively be suppressed. Further, since inclination of the impeller is suppressed, needless contact between the impeller and the casing is eliminated, and the impeller can rotate smoothly.

In the case where the outer peripheral face of the impeller is supported by the supporting device, the rolling element of the supporting device may be a tapered roller. In the case where a tapered roller is used, it is preferred that a small diameter side of the tapered roller is located at an upper face side of the impeller, and a large diameter side of the tapered roller is located at a lower face side of the impeller. When fuel is discharged upwards, it may be the case that greater pressure is exerted on the upper face of the impeller than on the lower face thereof By locating the large diameter side of the tapered roller at the lower face side of the impeller, downward force exerted on the impeller can be received by the supporting device.

In another aspect of the present teachings, the fuel pump may include a shaft passing from top to bottom through a center of the impeller. The impeller may be joined with the shaft in a manner allowing rotation. Alternatively, the impeller may be fixed to the shaft, and a shaft receiving member may be disposed in the casing, the shaft receiving member supporting the shaft in a manner allowing rotation. The impeller can rotate smoothly due to the provision of the shaft.

It is preferred that the shaft receiving member is formed at each end of the shaft and that these shaft receiving members are located opposite end faces of the shaft. For example, the end faces of the shaft may be formed in a cone shape, and a groove (a concave part) conforming with the cone shape of the shaft may be formed in the shaft receiving member. End parts of the shaft may be maintained in the grooves of the shaft receiving members.

In this fuel pump, both ends of the shaft fixed to the impeller are formed in a cone shape and are supported by the shaft receiving members. As a result, the area of contact between the shaft and the shaft receiving members can be small, and sliding resistance between the shaft and the shaft receiving members can be reduced.

In another aspect of the present teachings, the fuel pump may include a ball shaft fixed to the impeller, and have a shaft receiving member for supporting the ball shaft. It is preferred that the ball shaft is disposed so as to pass through the center of the impeller, and that a portion of the ball shaft protrudes from the upper and the lower faces of the impeller. It is preferred that the shaft receiving members are formed at both the upper and lower faces of the impeller.

In this fuel pump, a ball-shaped shaft is used as the shaft that is fixed to the impeller. Consequently, sliding resistance between the shaft and the shaft receiving members can be kept small. Further, use of the ball shaft allows cheap manufacture.

These aspects and features may be utilized singularly or, in combination, in order to make improved fuel pump. In addition, other objects, features and advantages of the present teachings will be readily understood after reading the following detailed description together with the accompanying drawings and claims. Of course, the additional features and aspects disclosed herein also may be utilized singularly or, in combination with the above-described aspect and features.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of a fuel pump of a first representative embodiment of the present teachings.

FIG. 2 schematically shows an example of a positional relationship between ball bearings, a driving coil, and an upper face side groove, these all being disposed in an upper inner face of a pump casing.

FIG. 3 is a plan view of an impeller.

FIG. 4 is a longitudinal sectional view of a fuel pump of a second representative embodiment of the present teachings.

FIG. 5 is a longitudinal sectional view of a fuel pump that is a variant of the second representative embodiment.

FIG. 6 is a longitudinal sectional view of a fuel pump of a third representative embodiment of the present teachings.

FIG. 7 is a longitudinal sectional view of a fuel pump that is a variant of the third representative embodiment.

DETAILED DESCRIPTION OF THE INVENTION First Representative Embodiment

Fuel pump 10 according to a first representative embodiment of the present teachings will be described. Fuel pump 10 is utilized in a motor vehicle, and is disposed within a fuel tank thereof. Fuel pump 10 is operated while submerged in fuel in the fuel tank and fuel pump 10 supplies the fuel in the fuel tank to an engine of the motor vehicle. As shown in FIG. 1, fuel pump 10 may comprise a circuit section 60 and a pump section 12. The up-down direction in FIG. 1 is the up-down direction when fuel pump 10 is disposed within the fuel tank (not shown).

The circuit section 60 may be provided with a circuit casing 16 and a base 62. A housing 18 has a substantially cylindrical shape. The circuit casing 16 is attached by means of caulking (mechanically deforming) or the like to an upper end 18 a of the housing 18. A discharge port 70 and a terminal 68 are formed on the circuit casing 16. The discharge port 70 opens in an upwards direction, and the terminal 68 is connected with an external power supply (not shown). A circuit chamber 63 is formed in the circuit casing 16. The circuit chamber 63 communicates with the discharge port 70.

The base 62 is housed in the circuit chamber 63. A motor controlling circuit 64 is mounted on the base 62. The motor controlling circuit 64 may comprise a plurality of electronic elements. The motor controlling circuit 64 converts, into three-phase power, direct power supplied from the external power supply via the terminal 68. The three-phase power that has been converted by the motor controlling circuit 64 is supplied to driving coil 40 via power supply line 66. Moreover, the motor controlling circuit 64 is preferably protected by non-conducting material (e.g., resin) that is resistant with respect to fuel.

The pump section 12 may be provided with a pump casing 14 and an impeller 20 housed within the pump casing 14. As shown in FIGS. 1 and 3, the impeller 20 is substantially disk shaped. A group of concavities (22 and 24) is formed in upper and lower aces of the impeller 20 in areas located inwardly from an impeller outer circumference face 25 s by a predetermined distance. The group of concavities (22 and 24) extends along the circumference direction of the impeller 20. The concavities (22 and 24) are repeated in a circumference direction. Bottom portions of the pair of upper concavities 24 and lower concavities 22 communicate via through-holes. The group of concavities (22 and 24) is separated by an outer peripheral wall of the impeller 20 from the outer circumference face 25 s of the impeller 20. A minute space (not shown in FIG. 1) is formed between the pump casing 14 and the outer circumference face 25 s of the impeller 20. This space is formed to allow the impeller 20 to rotate smoothly.

A through hole 27 is formed in a center of the impeller 20 and passes through the impeller 20 in its direction of thickness. A shaft 50 that is fixed at both ends to the pump casing 14 is inserted through the through hole 27. A bearing 52 is attached between the shaft 50 and the impeller 20, and is joined such that the impeller 20 can rotate with respect to the shaft 50 (i.e., the pump casing 14).

Moreover, a plurality of permanent magnets (26a and 26b) is disposed in the impeller 20. The permanent magnets (26 a and 26 b) are located in an area outwardly from the through hole 27 and inwardly from the group of concavities (22 and 24). First permanent magnets 26 a and second permanent magnets 26 b are disposed such that the upper faces of the first permanent magnets 26 a are North poles and the upper faces of the second permanent magnets 26 b are South poles. The first permanent magnets 26 a and second permanent magnets 26 b are disposed alternately in the circumference direction.

The pump casing 14 is attached by means of caulking (mechanically deforming) or the like to an inner side of a lower end 18 b of the housing 18. The pump casing 14 houses the impeller 20 such that it can rotate. The circuit casing 16 is mounted on pump casing 14, and the two are fitted together. Furthermore, an outer peripheral seal of the pump casing 14 and the circuit casing 16 can be obtained by means of resin welding, an O-ring, etc.

As shown in FIG. 2, an upper face groove 32 is formed in an inner face of the pump casing 14, this being a face opposite the upper face of the impeller 20 (hereinafter, this face will be referred to as an upper inner face of the pump casing). The upper face groove 32 is formed in the upper inner face of the pump casing 14 in an area directly facing the group of concavities 24 formed in the upper face of the impeller 20, this groove 32 extending in the direction of rotation of the impeller 20 from an upstream end 32 a to a downstream end 32 b. Fuel intake holes 30 a and 28 a are formed in a side face of the pump casing 14. The upstream end 32 a of the upper face groove 32 communicates with the fuel intake hole 30 a via an intake passage 30 formed in the pump casing 14. The downstream end 32 b of the upper face groove 32 communicates with the circuit chamber 63 of the circuit casing 16 via a discharge passage 36 formed in the pump casing 14.

Further, a plurality of driving coil 40 may be disposed at the upper inner face of the pump casing 14. The driving coil 40 is disposed in an area opposite the permanent magnets 26. Each driving coil 40 may comprise a core 43 and a coil 41 wound around the core 43. Power is supplied from the motor controlling circuit 64 to the coil 41 of the driving coil 40. The motor controlling circuit 64 converts the power supplied to each of the driving coil 40, thus causing the impeller 20 to rotate with respect to the pump casing 14. The shaft 50 and the bearing 52 are disposed at an inner side from the driving coil 40.

Furthermore, ball bearings 42 are provided at the upper inner face of the pump casing 14 at a location outwards with respect to the region having the driving coil 40, and inwards with respect to the region where the upper face groove 32 is formed. For example, the ball bearings 42 may be disposed in approximately the center between the driving coil 40 and the upper face groove 32. The number and location of the ball bearings 42 can be set as appropriate.

In the representative embodiment, as shown in FIG. 2, the ball bearings 42 are provided in three locations along the circumference direction of the impeller 20. That is, the ball bearings 42 are disposed at regular intervals around the center of the impeller 20 (i.e., spaced from one another at approximately 120°), and are at an identical distance from the center of the impeller 20. The provision of the ball bearings 42 at three locations along the circumference direction effectively prevents the impeller 20 from inclining. Further, disposing the ball bearings 42 equidistantly along the circumference direction causes approximately equal contact pressure between the impeller 20 and each of the ball bearings 42. Moreover, when the ball bearings 42 are located at the center between the driving coil 40 and the upper face groove 32, the ball bearings 42 effectively receive force that is exerted in a direction of thrust, this force being exerted on the impeller 20 by the driving coil 40 and by the fuel within the upper face groove 32.

A lower face groove 34 is formed in the inner face of the pump casing 14, this being a face opposite the lower face of the impeller 20 (hereinafter, this face will be referred to as a lower inner face of the pump casing). As with the upper inner face of the pump casing described above, the lower face groove 34 is formed in the lower inner face of the pump casing 14 in an area directly facing the group of concavities 22 formed in the lower face of the impeller 20, this groove 34 extending in the direction of rotation of the impeller 20 from an upstream end to a downstream end. The upstream end of the lower face groove 34 communicates with the fuel intake hole 28 a via an intake passage 28. The downstream end of the lower face groove 34 communicates with the circuit chamber 63 of the circuit casing 16 via a discharge passage 38.

Further, driving coil 40 is disposed at the lower inner face of the pump casing 14 in an area opposite the permanent magnets 26 of the impeller 20. Moreover, ball bearings 42 are provided outwards with respect to the area having the driving coil 40, and inwards with respect to the area where the lower face groove 34 is formed. The ball bearings 42 located at the lower inner face of the pump casing are disposed at the same location as the ball bearings 42 located at the upper inner face of the pump casing 14. Consequently, the impeller 20 is supported by the ball bearings 42 provided at its upper and lower faces.

In the fuel pump 10, the impeller 20 rotates when power is supplied to the driving coil 40. When the impeller 20 rotates, a revolving current of fuel is generated between the lower face groove 34 of the pump casing 14 and the concavities 22 formed in the lower face of the impeller 20. The pressure of the fuel rises as the fuel flows downstream, while revolving, along the lower face groove 34. While the fuel is being pressurized, fuel from the exterior is drawn inwards through the intake passage 28. The fuel that has been pressurized in the lower face groove 34 flows from the discharge passage 38 into the circuit chamber 63 of the circuit casing 16. The fuel in the circuit chamber 63 is delivered from the discharge port 70 to the exterior of the fuel pump 10.

A revolving current of fuel is also generated between the upper face groove 32 of the pump casing 14 and the concavities 24 in the upper face of the impeller 20. The pressure of the fuel rises as the fuel flows downstream along the upper face groove 32. While the fuel is being pressurized, fuel from the exterior is drawn inwards from the fuel intake hole 30 a to the intake passage 30. The fuel that has been pressurized in the upper face groove 32 flows from the discharge passage 36 into the circuit chamber 63 of the circuit casing 16. The fuel in the circuit chamber 63 is delivered from the discharge port 70 to the exterior of the fuel pump 10.

In the fuel pump 10, fuel is drawn into the upper and lower faces of the impeller 20, and is discharged from the upper and lower faces of the impeller 20. Consequently, the impeller 20 does not readily become inclined. Further, there is communication between the bottom portions of the concavities 24 formed in the upper face of the impeller 20 and the bottom portions of the concavities 22 formed in the lower face of the impeller 20. Consequently, the fuel flowing at the upper face and the lower face has approximately identical pressure, and as a result the impeller 20 is prevented from inclining.

As is clear from the above description, the fuel pressure from the fuel within the concavities (22 and 24), and the magnetic force from the driving coil 40 both operate upon the impeller 20. These forces do not operate uniformly in the circumference direction of the impeller 20, and consequently a force for causing the impeller 20 to become inclined operates thereupon. In the fuel pump 10 of the present embodiment, the upper and lower faces of the impeller 20 are supported by the ball bearings 42 provided in the pump casing 14. As a result, even if force operates on the impeller 20 to cause it to become inclined, the impeller 20 is supported by its contact with the ball bearings 42, and this prevents the impeller 20 from inclining. Consequently, the impeller 20 does not make direct contact with the inner face of the pump casing 14. Further, the ball bearings 42 revolve while making contact with the impeller 20, and consequently sliding resistance between the ball bearings 42 and the impeller 20 can be kept small. The impeller 20 can rotate smoothly as a result, and pump efficiency can be improved.

Moreover, since the impeller 20 is supported by the ball bearings 42, it is possible to reduce abrasion of the upper and lower faces of the impeller 20, or abrasion of the pump casing 14. As a result, the change of the space between the impeller 20 and the pump casing 14 is suppressed, and increase in the quantity of leakage as time passes is suppressed. Pump efficiency is thus prevented from decreasing with the passage of time.

Furthermore, the fuel that has been drawn into the fuel pump 10 passes through the circuit chamber 63 and is discharged to the exterior from the discharge port 70. Consequently, even if the motor controlling circuit 64 becomes heated by the delivery of power to the driving coil 40, the motor controlling circuit 64 can be cooled by the fuel flowing through the circuit chamber 63.

Second Representative Embodiment

The following description concentrates on parts that differ from the first representative embodiment. The second representative embodiment differs from the first representative embodiment in the following points; (1) the ball bearings 42 are not provided, and (2) a shaft is fixed in the center of the impeller 20, and the impeller 20 rotates integrally with the shaft. However, the second representative embodiment, also, may be equipped with the ball bearings 42 that support the impeller 20.

As shown in FIG. 4, a shaft 72 is fixed in the impeller 20 and passes through the center thereof from top to bottom. The method of fixing the shaft 72 to the impeller 20 can be, for example, press fitting the shaft 72 into a through hole of the impeller 20. Both ends of the shaft 72 are cone shaped, and are supported in shaft receiving members 74 mounted in the pump casing 14. A groove 74 a that conforms with the cone shape of the shaft 72 is formed in each shaft receiving member 74, and end parts of the shaft 72 are maintained (or supported) in the grooves 74 a in a manner allowing rotation.

There is a small area of contact between the shaft 72 and the shaft receiving members 74 in the configuration of the second representative embodiment. As a result, sliding resistance between the shaft 72 and the shaft receiving members 74 can be reduced. Consequently, as with the first representative embodiment, the impeller 20 can rotate smoothly, and high pump efficiency can be achieved.

As shown in FIG. 5, a ball shaft 76 can be used as the shaft fixed to the impeller 20. The ball shaft 76 can be supported by shaft receiving members 78 a and 78b mounted in the pump casing 14. With this configuration, also, it is possible to reduce sliding resistance between the ball shaft 76 and the shaft receiving members 78 a and 78 b, and high pump efficiency can be achieved. Further, there is no need for special processing of the shaft when the ball shaft 76 is used as the shaft fixed to the impeller 20, and consequently the fuel pump can be manufactured more cheaply.

Third Representative Embodiment

The following description concentrates on parts that differ from the first representative embodiment. The third representative embodiment differs from the first representative embodiment in the following points; (1) a though hole does not pass from top to bottom through the center of the impeller 20, and (2) the impeller 20 is supported along its outer peripheral face by the pump casing 14.

As shown in FIG. 6, roller bearings 80 are disposed along a circumference direction, in at least three locations, of the inner face of the pump casing 14 located opposite the outer peripheral face of the impeller 20. The roller bearings 80 may, for example, be disposed equidistantly along the circumference direction of the impeller 20, supporting the outer peripheral face of the impeller 20 at three or more locations.

Tapered rollers may be used in the rollers of the roller bearings 80. In the case where tapered rollers are used, it is preferred that the outer peripheral face of the impeller 20 is formed in a truncated cone shape that grows narrower in a downward direction. It is preferred that the portions that are greater in diameter of the tapered rollers of the roller bearings 80 make contact with a lower face side of the impeller 20, and that the portions of the tapered rollers that are smaller in diameter make contact with an upper face side of the impeller 20. By this means, the roller bearings 80 can receive the load in a direction of thrust of the impeller 20.

With the configuration of the third representative embodiment, the roller bearings 80 suppress any inclining of the impeller 20 that would occur, and the impeller 20 is prevented from making direct contact with the pump casing 14. Consequently, as with the first representative embodiment, the impeller 20 can rotate smoothly, and high pump efficiency can be achieved.

Further, as shown in FIG. 7, roller bearings 82 can be used in a supporting device for supporting the outer peripheral face of the impeller 20.

Finally, although the preferred representative embodiments have been described in detail, the present embodiments are for illustrative purpose only and not restrictive. It is to be understood that various changes and modifications may be made without departing from the spirit or scope of the appended claims. In addition, the additional features and aspects disclosed herein also may be utilized singularly or in combination with the above aspects and features. 

1. A fuel pump comprising: a substantially disk-shaped impeller having permanent magnets disposed therein, a casing for housing the impeller such that the impeller can rotate, the casing having a driving coil disposed at a location opposite the permanent magnets of the impeller, and wherein the driving coil causes the impeller to rotate when power is supplied to the driving coil, and a supporting device supporting the impeller and being disposed in at least one location in an inner face of the casing, this inner face of the casing being located opposite an upper face, a lower face, and an outer peripheral face of the impeller, and wherein the supporting device has a rolling element, this rolling element making rolling contact with the impeller.
 2. The fuel pump as in claim 1, wherein: a first group of concavities is formed in an upper face of the impeller along a region in the vicinity of an outer periphery of the impeller, and the first group of concavities is formed outwards with respect to the permanent magnets, a second group of concavities is formed in a lower face of the impeller along a region in the vicinity of an outer periphery of the impeller, and the second group of concavities is formed outwards with respect to the permanent magnets, a first groove is formed in the inner face of the casing opposite the upper face of the impeller, this first groove being formed in a region opposite the first group of concavities in the impeller and extending from an upstream end to a downstream end, a second groove is formed in the inner face of casing opposite the lower face of the impeller, this second groove being formed in a region opposite the second group of concavities in the impeller and extending from an upstream end to a downstream end, and a fuel intake passage and a fuel discharge passage are formed in the casing, wherein the fuel intake passage communicates between the vicinity of the upstream end of the first groove and the exterior of the casing, and between the vicinity of the upstream end of the second groove and the exterior of the casing, and wherein the fuel discharge passage communicates between the vicinity of the downstream end of the first groove and the exterior of the casing, and between the vicinity of the downstream end of the second groove and the exterior of the casing.
 3. The fuel pump as in claim 2, wherein: the supporting device is disposed in the inner face of the casing opposite both the upper and the lower face of the impeller, and the supporting device supports the impeller at a region outwards with respect to the region having the permanent magnets, and inwards with respect to the region having the concavities formed therein.
 4. The fuel pump as in claim 1, wherein the supporting device is disposed in at least three locations in the inner face of the casing opposite the outer peripheral face of the impeller.
 5. The fuel pump as in claim 4, wherein the rolling element of the supporting device is a tapered roller, and a small diameter side of the tapered roller is located at an upper face side of the impeller, and a large diameter side of the tapered roller is located at a lower face side of the impeller.
 6. The fuel pump as in claim 1, the fuel pump further comprising: a shaft attached to the impeller and having both end faces formed in a cone shape, a shaft receiving member formed at each end of the shaft, each shaft receiving member having a shaft receiving face located opposite each end face of the shaft, and wherein a groove conforming with the cone shape is formed in each shaft receiving face, and an end part of the shaft is supported in the groove of the shaft receiving face.
 7. The fuel pump as in claim 1, the fuel pump further comprising: a ball shaft attached to the impeller, and a shaft receiving member formed at each of the upper face and the lower face of the impeller, this shaft receiving member supporting the ball shaft.
 8. A fuel pump comprising a substantially disk-shaped impeller having permanent magnets disposed therein, a casing for housing the impeller such that the impeller can rotate, the casing having a driving coil disposed at a location opposite the permanent magnets of the impeller, wherein the driving coil causes the impeller to rotate when power is supplied to the driving coil, a shaft attached to the impeller and having both end faces formed in a cone shape, and a shaft receiving member formed at each end of the shaft, the shaft receiving member having a shaft receiving face located opposite each end face of the rotary shaft, and wherein a groove conforming with the cone shape of the shaft is formed in each shaft receiving face, and an end part of the shaft is supported in the groove of the shaft receiving face.
 9. A fuel pump comprising: a substantially disk-shaped impeller having permanent magnets disposed therein, a casing for housing the impeller such that the impeller can rotate, the casing having a driving coil disposed at a location opposite the permanent magnets of the impeller, wherein the driving coil causes the impeller to rotate when power is supplied to the driving coil, a ball shaft attached to the impeller, and a shaft receiving member formed at each of an upper face and a lower face of the impeller, this shaft receiving member supporting the ball shaft. 